This invention is directed to apparatus and methods for measuring a plurality of electrical signals from an electrode array preferably situated in the body of a patient, and is especially suited for measuring a plurality of weak electrical signals emanating from a patient""s heart using intracardiac non-contact electrodes.
Cardiac arrhythmias, the most common of which is ventricular tachycardia (VT), are a leading cause of death. In a majority of patients, VT originates from a 1 mm to 2 mm lesion located close to the inner surface of the heart chamber. One of the treatments for VT comprises mapping the electrical pathways of the heart to locate the lesion followed by ablation of the active site.
Commonly assigned U.S. Pat. No. 5,546,951; and PCT application WO 96/05768 and its corresponding U.S. patent application Ser. No. 08/793,371 filed on May 14, 1997, all of which are incorporated herein in their entirety by reference, disclose methods for sensing an electrical property of heart tissue, for example, local activation time, as a function of the precise location within the heart. The data are acquired with one or more catheters having electrical and location sensors in their distal tips that are advanced into the heart. Electrical signals are generally acquired with an electrode located at the catheter distal tip after determining that the tip is in stable and steady contact with the endocardium. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. patent application Ser. Nos. 09/122,137 and 09/357,559 filed on Jul. 24, 1998 and Jul. 22, 1999, respectively, which are also incorporated herein in their entirety by reference. As indicated in these applications, location and electrical activity is preferably initially measured at about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map is often combined with data taken at additional points in order to generate a more comprehensive map of the heart""s electrical activity. In clinical settings, it is not uncommon to accumulate data at 100 or more sites to generate a detailed, comprehensive map of heart chamber electrical activity. The generated detailed map may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart""s electrical activity and to restore normal heart rhythm.
Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096 which is incorporated herein in its entirety by reference, maps depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart.
A drawback with mapping a cardiac chamber using a catheter containing only a single, distal tip electrode is the long period of time required to accumulate data on a point-by-point basis over the requisite number of points required for a detailed map of the chamber as a whole. Accordingly, multiple-electrode catheters have been developed to simultaneously measure electrical activity at multiple points in the heart chamber. Cardiac electrical activity data has been acquired with multi-electrode catheters using contact as well as non-contact methods.
U.S. Pat. No. 5,487,391, directed to systems and methods for deriving and displaying the propagation velocities of electrical events in the heart, is illustrative of contact methods found in the art. In the system disclosed in the ""391 patent, the electrical probe is a three-dimensional structure that takes the form of a basket. In the embodiment illustrated in the ""391 patent, the basket is composed of 8 splines, each of which carries eight electrodes, for a total of 64 electrodes in the probe. The basket structure is designed such that when deployed, its electrodes are held in intimate contact against the endocardial surface. A problem with the catheters disclosed in the ""391 patent is that they are both difficult and expensive to produce. The large number of electrodes in such catheters is also very demanding of the data recording and processing subsystem. There are additional complexities associated with the deployment and withdrawal of these catheters, and increased danger of blood coagulation.
U.S. Pat. No. 5,848,972 to Triedman et al. discloses a method for endocardial activation mapping using a multi-electrode catheter. In the method of the ""972 patent, a multi-electrode catheter, preferably, a 50-electrode Webster-Jenkins(trademark) basket catheter from Cordis-Webster of Baldwin Park, Calif., is advanced into a chamber of the heart. Anteroposterior (AP) and lateral fluorograms are obtained to establish the position and orientation of each of the electrodes. Electrograms are recorded from each of the electrodes in contact with the cardiac surface relative to a temporal reference such as the onset of the P-wave in sinus rhythm from a body surface ECG. Interestingly, Triedman et al. differentiate between those electrodes that register electrical activity and those that do not due to absence of close proximity to the endocardial wall. After the initial electrograms are recorded, the catheter is repositioned, and fluorograms and electrograms are once again recorded. An electrical map is then constructed from the above information.
U.S. Pat. No. 4,649,924 to Taccardi discloses a method for the detection of intracardiac electrical potential fields. The ""924 patent is illustrative of the non-contact methods that have been proposed to simultaneously acquire a large amount of cardiac electrical information. In the method of the ""924 patent, a catheter having a distal end portion is provided with a series of sensor electrodes distributed over its surface. The electrodes are connected to insulated electrical conductors for connection to signal sensing and processing means. The size and shape of the catheter distal end portion are such that the electrodes are spaced substantially away from the wall of the cardiac chamber. The electrodes are preferably distributed on a series of circumferences lying in planes spaced from each other and perpendicular to the major axis of the end portion of the catheter. At least two additional electrodes are provided adjacent the ends of the major axis of the end portion. The ""924 patent discloses a single exemplary embodiment in which the catheter comprises eight electrodes spaced equiangularly on each of four circumferences. Thus, in that exemplary embodiment, the catheter comprises 34 electrodes (32 circumferential and two end electrodes). The method of the ""924 patent is said to detect the intracardiac potential fields in only a single cardiac beat.
PCT application WO 99/06112 to Rudy, the disclosure of which is incorporated herein by reference, discloses an electrophysiological cardiac mapping system and method based on a non-contact, non-expanded multi-electrode catheter. Electrograms are obtained with catheters having from 42 to 122 electrodes. In addition to the above-described problem of complexity of multi-electrode catheters, the Rudy method requires prior knowledge of the relative geometry of the probe and the endocardium, which must be obtained via an independent imaging modality such as transesophogeal echocardiography. In the Rudy method, after the independent imaging, non-contact electrodes are used to measure cardiac surface potentials and construct maps therefrom.
U.S. Pat. No. 5,297,549 to Beatty et al., the disclosure of which is incorporated herein by reference, discloses a method and apparatus for mapping the electrical potential distribution of a heart chamber. In the Beatty method, an intra-cardiac multielectrode mapping catheter assembly is inserted into the heart. The mapping catheter assembly includes a multi-electrode array with an integral reference electrode, or, preferably, a companion reference catheter. In use, the electrodes are deployed in the form of a substantially spherical array. The electrode array is spatially referenced to a point on the endocardial surface by the reference electrode or by the reference catheter which is brought into contact with the endocardial surface. The preferred electrode array catheter is said to carry at least 24 individual electrode sites.
U.S. Pat. No. 5,311,866 to Kagan et al. discloses a heart mapping catheter assembly including an electrode array defining a number of electrode sites. The mapping catheter assembly also comprises a lumen to accept a reference catheter having a distal tip electrode assembly which may be used to probe the heart wall. In the preferred construction, the mapping catheter comprises a braid of insulated wires, preferably having 24 to 64 wires in the braid, each of which are used to form electrode sites. The catheter is said to be readily positionable in a heart to acquire electrical activity information from a first set of non-contact electrode sites and/or a second set of in-contact electrode sites.
U.S. Pat. Nos. 5,385,146 and 5,450,846 to Goldreyer disclose a catheter that is said to be useful for mapping electrophysiological activity within the heart. The catheter body has a distal tip which is adapted for delivery of a stimulating pulse for pacing the heart or an ablative electrode for ablating tissue in contact with the tip. The catheter further comprises at least one pair of orthogonal electrodes. The orthogonal electrodes are coupled in a pair-wise fashion to differential amplifiers to generate difference signals said to be indicative of the local cardiac electrical activity adjacent the orthogonal electrodes.
U.S. Pat. No. 5,662,108 to Budd et al. discloses a process for measuring electrophysiological data in a heart chamber. The method involves, in part, positioning a set of active and passive electrodes into the heart, supplying current to the active electrodes to generate an electric field in the heart chamber, and measuring the resultant electric field at the passive electrode sites. In one of the disclosed embodiments, the passive electrodes are contained in an array positioned on an inflatable balloon of a balloon catheter. In preferred embodiments, the array is said to have from 60 to 64 electrodes.
Commonly assigned U.S. patent application Ser. No. 09/506,766 filed on Feb. 18, 2000, the disclosure of which is incorporated herein by reference, discloses a novel apparatus and method for rapidly generating an electrical map of a chamber of a heart. In one embodiment, the apparatus and method of the ""766 application utilize a catheter including a contact electrode positioned at the catheter distal tip and an array of non-contact electrodes, preferably comprising from about 12 to about 32 electrodes, positioned proximal from the catheter distal tip. The catheter further includes at least one and preferably two location sensors. The catheter is used for rapidly generating an electrical map of the heart within at least one cardiac cycle and preferably includes cardiac ablation and post-ablation validation.
Multi-electrode methods to acquire cardiac electrical signals offer the potential for reducing the time required to generate an electrical map, especially relative to single point contact measurements. A problem with non-contact methods, however, is the weakness of the electrical signal compared to contact measurements, particularly as the electrodes become further removed from the endocardium. Frequently, the magnitude of a non-contact signal is only slightly greater than the noise level. Thus, it is often difficult to accurately discriminate the electrical potential at adjacent electrodes, and this has negative implications on the accuracy of the cardiac map produced from such measurements. Thus, there exists a need for more accurate measurements of weak electrical signals, particularly of the type and of the magnitude encountered in non-contact intracardiac measurements.
One aspect of the invention is directed to an apparatus for measuring a plurality of electrical signals from an electrode array. The apparatus of the invention comprises a first amplifier for measuring a voltage at a first electrode of the array. The apparatus further comprises a cascade of differential amplifiers, each of which measures an analog voltage difference between two successive electrodes in said array. The voltage, Vn, at electrode n is given by the expression:             V      n        =                  a        1            +                        ∑                      i            =            2                    n                ⁢                  xe2x80x83                ⁢                  a          i                      ,
wherein a1, is the voltage at the first electrode as measured by the first amplifier and each ai is a differential voltage between electrode i and electrode (ixe2x88x921) of the array as measured by the differential amplifiers.
In some embodiments, the apparatus of the invention further comprises a computing processor to compute the voltages at the electrodes.
Another aspect of the invention is directed to an apparatus for measuring electrical signals emanating from a body of a patient. The apparatus comprises a catheter which comprises an electrode array, preferably on its distal end. The apparatus of the invention further comprises a first amplifier for measuring a voltage from a first electrode of the array, and a cascade of differential amplifiers, each of which measures a voltage difference between two successive electrodes in the array. The voltage, Vn, at electrode n is given by the expression:             V      n        =                  a        1            +                        ∑                      i            =            2                    n                ⁢                  xe2x80x83                ⁢                  a          i                      ,
wherein a1, is the voltage at the first electrode as measured by the first amplifier and each ai, is a differential voltage between electrode i and electrode (ixe2x88x921) of the array as measured by the differential amplifiers.
In some embodiments, the apparatus of the invention further comprises a computing processor to compute the voltages at the electrodes.
In some embodiments, the catheter electrode array comprises at least one contact electrode and a plurality of non-contact electrodes. In such embodiments, the first amplifier is preferably used to measure the signal at the contact electrode.
In some embodiments, the catheter used in the apparatus of the invention further comprises at least one position sensor. In some embodiments, the catheter comprises a first position sensor proximate the catheter distal tip and a second position sensor proximal to the electrode array. The at least one position sensor is preferably selected from acoustic sensors, magnetic sensors, electromagnetic sensors or combinations thereof. At least one of the position sensors is preferably an electromagnetic position sensor.
Another aspect of the invention is directed to a method for measuring a plurality of electrical signals from an electrode array. The method of the invention comprises providing a first amplifier for measuring a voltage at a first electrode of the array and a cascade of differential amplifiers, each of which measures a voltage difference between two successive electrodes in the array. The method further comprises computing a voltage at each of the electrodes, wherein the voltage, Vn, at electrode n is given by the expression:             V      n        =                  a        1            +                        ∑                      i            =            2                    n                ⁢                  xe2x80x83                ⁢                  a          i                      ;
wherein a1 is the voltage at the first electrode as measured by the first amplifier and each ai is a differential voltage between electrode i and electrode (ixe2x88x921) of the array as measured by the differential amplifiers. The method is preferably employed to measure a plurality of electrical signals emanating from a body of a patient, and more preferably, from a patient""s heart.
In some embodiments, the method of the invention further comprises the steps of providing a catheter having an electrode array positioned at its distal end, and advancing the catheter distal end into the patient""s heart.
In some embodiments, the electrical signals measured by the method of the invention are used to determine an electrical characteristic of the patient""s tissue, such as the peak voltage or the local activation time of cardiac tissue of the patient""s heart. The method of the invention further optionally comprises generating a map of the electrical characteristic of a patient""s tissue. The method of the invention may further comprise diagnosing a disease state of the tissue from the map of the electrical characteristic, and it may also further comprise treating the tissue.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: